A system under development from Validus International to record near-bit directional surveys and transmit them to surface uses two new technologies that promise a substantial improvement in directional drilling operations.
The downhole directional tool uses a Nonrotating Adjustable Stabilizer (NAS) design to precisely control curvature rate. Directional drilling operations are controlled automatically by Directional Solution (DS) software, which computes the position of the borehole after each survey and determines the optimum 3-D circular arc trajectory needed to hit directional or horizontal targets. The combination of these two technologies allows the driller to optimize performance of the drill bit while the NAS and DS optimize drilling operations.
These novel approaches to curvature-rate control and trajectory planning will provide significant benefits to the operator:
The NAS/DS will have unprecedented targeting precision. This can provide enormous economic benefits in the appropriate application;
The inherent hard-rock directional and horizontal capabilities of the system will also provide large savings over the use of conventional motors. This is especially true for well plans that require higher curvature rates; and
Autonomous trajectory control, precise curvature-rate control and a strategy of drilling each joint or stand at a constant curvature rate will combine to provide the least tortuous path possible. In areas where tortuosity requires extensive remediation, this feature can provide significant economic benefits.
The NAS/DS system is designed to be an efficient and robust directional drilling tool. A single bottomhole assembly is used to drill to the kickoff point, to drill the directional and tangent sections, to drill the horizontal build curve and to drill the horizontal producing interval. The system is compatible with all commercially offered bits and imposes no known constraints on bit weight, rotary speed or hydraulics.
The NAS/DS uses a unique system to direct the path of a borehole. Eccentricity of the tool is precisely controlled using individually adjustable stabilizer blades located approximately 2 ft (.61 m) above the bit. This mechanism allows precise control of the curvature rate and toolface angle. Curvature can be set at any rate between 0° and 15°/100 ft (30.5 m). The full length of each joint or stand is drilled at a uniform curvature rate and toolface angle. Porpoising action is eliminated, unlike typical RSS control systems that attempt to hold inclination angles and azimuths. The NAS/DS uses a closed-loop, error-correction routine to fine tune curvature rate and toolface settings and to provide extremely high targeting precision.
The NAS/DS system uses the DS software to provide autonomous control of targeting trajectories. This program calculates the new optimum path after each survey. It is usually quite similar to the original plan, but initiates from the actual location of the last survey. This strategy eliminates the doglegs required to first deflect the well bore back toward the original, pre-drilling directional plan and then again to realign the well bore with the path of the original objective.
The software computes the optimum path through the next three directional targets or through up to two directional targets located above a horizontal target. The solution algorithm also optimizes the path to produce the least possible rotational torque. The combination of curvature-rate control and autonomous targeting provides high targeting precision and minimum wellbore tortuosity. The system will create a new industry standard for targeting precision. It will routinely hit directional targets within one foot and track horizontal target planes within a few inches.
The system is a standalone directional and horizontal drilling system that can also be run with any third-party logging-while-drilling system to obtain formation evaluation measurements. The system consists of a Non-rotating Adjustable Stabilizer (NAS) module above the bit, a flex joint and a Communications Link (CL) module above. Survey measurements in the NAS represent a point that is 4 ft to 5 ft above the bit. NAS data and measurements are transmitted electromagnetically (EM) to the CL and with mud pulses to the surface. The system includes a surface pulser that communicates with the CL and then to the NAS using EM transmissions. The two-way communications do not constrain operations and can be sent while drilling. The autonomous downhole control minimizes communication requirements. Downlinks are used to change targets or other directional data and to send special operational commands.

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